Regenerative circuit for cold cathode vacuum tubes



April 10, 1962 A. M. SKELLETT REGENERATIVE CIRCUIT FOR COLD CATHODE VACUUM TUBES TEE. 4? T1 -Z- United States atent 3,029,395 Patented Apr. 10, 1962 thee 3,029,395 REGENERATIVE CIRCUIT FOR COLD CATHODE VACUUM TUBES Albert M. Skellett, Madison, N .J assignor to Tung-Sol Electric Inc., a corporation of Delaware Filed June 22, 1959, Ser. No. 822,102 7 Claims. (Cl. 330-112) The present invention relates to cold cathode vacuum tube devices, more particularly to circuits incorporating such devices and comprises a novel regenerative circuit that includes an amplifier having a cold cathode. Cold cathodes employed in vacuum tube amplifiers and the like comprise a metal base or sleeve of nickel or the like coated with a porous sponge-like layer containing mag nesium oxide. Such coating has the characteristic of copious and self-sustaining electron emission once the emission is initiated and provided there is present an electrode at a higher potential for collection of the emitted electrons. The new regenerative circuit includes an amplifier or oscillator tube provided with such type cathode and includes circuit elements connected to the sustaining grid for augmenting the voltage swing of such grid when an alternating signal is impressed upon the control grid of the tube at'a predetermined frequency or frequency r n Briefly the new c-ircuit-corn-prisesa frequency responsive network connected in series with a resistor between the sustaining grid of a cold cathode vacuum tube and the source of positive bias potential for the sustaining grid. The frequency responsive network may be a circuit resonant at a preselected frequency to give maximum impedance at such frequency or may be a filter type notwork having wider frequency response.

For a better understanding of the invention and of circuits embodying the same reference may be had to the accompanying drawing of which:

FIG. 1 is a circuit diagram representing one embodiment of the invention;

FIGS. 2 and 3 are similar circuit diagrams representing other embodiments of the invention; and

FIG. 4 is a diagrammatic sectional view through the cold cathode tube of the circuits of FIGS. 1 to 3 illustrative of the construction thereof.

Referring first to FIG. 4, the cold cathode vacuum tube of the circuit may comprise an outer envelope 2 of glass or the like having mounted therein an electrode structure comprising an anode 4, a cathode indicated generally at 6, an inner grid 8, a second grid 10 encompassing the grid 8, and a third grid 12 encompassing the grid 10. The grids 8, 10 and 12 are mounted on suitably aligned posts 14 and aligned with the posts 14 is a filament 16 supported from a rod 18 and adapted for use in initiating emission from the coating of the cathode. The cathode comprises a sleeve 20 of nickel having an outer coating 22 thereon of magnesium oxide in porous sponge-like form. Within the sleeve 20 is a filament 24 used only for processing the tube when initially constructed and not used thereafter.

In FIGS. 1, 2 and 3 the cold cathode vacuum tube has been shown conventionally but the elements thereof are identified by the reference numerals used in FIG. 4.

In FIG. 1 the cold cathode vacuum tube 26 is shown with its anode 4 connected through the primary winding of an output transformer 28 to the positive terminal of a source 30 of direct current energy, and with its cathode 6 connected to ground and to the negative terminal of source 30. The inner grid 8, which in the circuit of FIG. 1 is the sustaining grid, is connected through a resistor 32 and network 34 to the positive terminal of the source 30. The second grid 10, which is the control grid in the circuit of FIG. 1 is connected through a capacitor 36 to a source of control signals and is connected through a resistor 38 to a point on the source 30 of above ground potential. The outer grid 12 which serves as a screen grid in the circuit of FIG. 1, is connected to the source 30 at a point of potential intermediate that of the control grid and of the anode.

In accordance with the invention the network 34 in the sustaining grid circuit is a frequency responsive element comprising a parallel arrangement of an inductor 40 and capacitor 42 tuned for parallel resonance at a preselected frequency. The function of the network 34 will become apparent from the following discussion.

When the tube 26 is drawing current some electrons are collected by the sustaining grid and other electrons pass through that grid to the other electrodes of the tube. Thus a small current flows in the circuit including the resistor 32 and network 34. When the control grid is made more positive more of the electrons from the cathode pass through the sustaining grid to the electrodes of the tube and accordingly the current to the sustaining grid is reduced. This results-in a higher sustaining grid potential. The higher potential on the sustaining grid attracts more electrons from the cathode and hence tends to cause some regeneration Thus the higher the impedance in the sustaining grid'circuit the greater will be the regeneration of the tube. By making the network 34 frequency responsive so as to have maximum impedance at a selected frequency the voltage swing on the sustaining grid will be enhanced at such frequency making the circuit a truly regenerative circuit suitable for use in amplifiers, oscillators, and the like.

Other frequency responsive networks could be substltuted for the specific circuit 34 shown in FIG. 1. When a response at high frequencies is desired, for example, the frequency responsive network could be a simple inductor as in the specific circuit illustrated in FIG. 2 to which reference may now be had.

In FIG. 2 the cold cathode vacuum tube of the circuit is indicated at 44. Constructionally it may be the same as that of FIG. 4 and is shown like tube 26 of FIG. 1 except for a difference in the grid connections. In FIG. 2 the first grid 8 and the third grid 12 are connected toge ther to serve as the control grid of the circuit. For this purpose they are connected through the capacitor 36 to the input terminal for the control signal and through resistor 38 to a point on the source 30 of above ground potential. In this embodiment of the invention the second grid 10 serves as the sustaining grid and that grid is connected through an adjustable resistor 46 and inductor 48 to a point on the source 30 intermediate the potential of the control grid and of the anode, which latter is connected as in FIG. 1, through the primary winding of output transformer 28 to the positive terminal of the source 39. With the inductor 48 in the sustaining grid circuit regeneration will occur at high frequencies, the higher the frequency the greater the regeneration. The principle of operation of the circuit of FIG. 2 is substantially like that of PEG. 1 in that, with increase in potential on the control grid the current to the sustaining grid is reduced with consequent increase in potential on that grid and such increase in potential further augments cathode emission. The inductor 48 in the sustaining grid circuit enhances the voltage swing of the sustaining grid with increase in frequency.

In the circuit of FIG. 3, to which reference may be had, the frequency responsive network in the circuit of the sustaining grid comprises two tunable circuits 50 and 52 inductively coupled together. Circuit 50 comprises a capacitor 54 and variable resistor 56 connected in series across an inductor 58 and circuit 52 comprises an inductor 60 coupled to inductor 53 and connected in series aoaaaes with a variable resistor 62 and capacitor 64. The remainder of the circuit of FIG. 3, being the same as that of FIG. 2 needs no description. With the circuits 5t} and 52 tuned to the same frequency, high impedance over a relatively wide band of frequencies may be obtained by adjustment of resistors 56 and 62 to give the proper circuit Qs. Thus regeneration can be obtained with the circuit of FIG. 3 over a Wider range than with the circuit of FIG. 1.

Obviously the network 3-4 of FIG. 1 could be substituted for the inductor 48 in the particular circuit of FIG. 2 and for the coupled circuits 50 and 52 of FIG. 3. Conversely the inductor 48 of FIG. 2 could be substituted for the network 34 in the circuit of FIG. 1. Also frequency responsive networks other than those illustrated could be employed.

The invention has now been described in connection with the two embodiments thereof. Other circuit arrangement embodying the invention will be apparent to those skilled in the art.

The following is claimed:

1. The combination with a cold cathode vacuum tube having a cathode of the type comprising a metal base having a porous sponge-like oxide coating thereon adapted to emit a self-sustaining stream of electrons once emission is initiated, a sustaining grid biased positively with respect to the cathode, at least one control grid and an anode, of means for enhancing the voltage swing of the sustaining grid at a preselected frequency range, said means comprising a frequency responsive network connected to the sustaining grid and through which the positive bias is impressed upon such grid.

2. The combination according to claim 1 including a stabilizing resistor connected in series with said network.

3. The combination according to claim 1 wherein said network comprises a parallel arrangement of inductor and capacitor tuned for maximum impedance within the selected frequency range.

4. A regenerative circuit comprising a source of direct current potential, :1 cold cathode vacuum tube amplifier having a cathode of the type comprising a metal base having a porous sponge-like oxide coating thereon adapted to emit a self-sustaining stream of electrons once emission is initiated, a sustaining grid, at least one control grid and an anode, the negative terminal of said source being connected to said cathode, connections between said source and said sustaining grid and between said source and said anode to maintain said sustaining grid and anode at above cathode potential and a frequency responsive network in the connection between said sustaining grid and said source.

5. The circuit according to claim 4 including a stabilizing resistor in series with said network in said last mentioned connection.

6. The circuit according to claim 4 wherein said network comprises a resonant circuit tuned for maximum impedance at a preselected frequency.

7. The circuit according to claim 4 wherein said network comprises a pair of coupled circuits tuned for maximum impedance over a preselected band of frequencies.

References Cited in the file of this patent UNITED STATES PATENTS 2,426,681 Adler Sept. 2, 1947 2,513,727 Koch July 4, 1950 2,577,461 Greefkes Dec. 4, 1951 2,621,264 Hultberg Dec. 9, 1952 2,675,432 Pan Apr. 13, 1954 2,802,127 Dobischek Aug. 6, 1957 2,842,706 Dobischek July 8, 1958 

1. THE COMBINATION WITH A COLD CATHODE VACUUM TUBE HAVING A CATHODE OF THE TYPE COMPRISING A METAL BASE HAVING A POROUS SPONGE-LIKE OXIDE COATING THEREON ADAPTED TO EMIT A SELF-SUSTAINING STREAM OF ELECTRONS ONCE EMISSION IS INITIATED, A SUSTAINING GRIDE BIASED POSITIVELY WITH RESPECT TO THE CATHODE, AT LEAST ONE CONTROL GRIDE AND AN 